Imaging features of benign and malignant renal tumours. Keys in differentiating renal masses.

1. Renal Tumour Imaging
Dr. Soe Moe Htoo
Radiology Resident
1

2. Introduction/Epidemiology
• The detection rate of renal masses has increased in the last decades
owing to the widespread use of CT and MRI.
• Accurate characterization of renal masses is essential to ensure
appropriate management.
• Renal masses  cystic or solid lesions
• 80% of solid masses are malignant.
• Therefore, a solid, enhancing mass must be considered malignant
unless proven otherwise.
2

3. • Renal cell carcinoma (RCC) is the most common malignant renal
tumour
• The most common subtype of RCC is the clear cell RCC.
• Other subtypes are papillary (basophilic and eosinophilic) and
chromophobe RCCs with about 25% of renal cortical tumours.
• Other malignant masses are transitional cell carcinoma (TCC),
lymphoma (primary and more frequent secondary), metastases from
carcinoma and primary/secondary sarcoma.
• Primary tumours of the lung, breast and gastrointestinal tract are the
most common sources of renal metastases.
• Benign tumours account for approximately 20% of all solid renal
cortical tumours.
3

4. Imaging parameters of renal masses
I. Detection of lesions:
• Because of better soft-tissue contrast, the tumour detection rate
seems better with MR.
• But according to the literature, renal lesions with a diameter of more
than 2 cm, CT shows a similar detection rate.
4

5. II. Size, shape and contour:
• Renal masses with a diameter of <4 cm are defined as small renal
masses.
• The smaller the mass is, the greater the chance of being benign.
• Among malignant masses, greater size correlates with higher
pathological grade.
• Unsharpened borders of a solid tumour are nearly always a sign of
malignancy (except: inflammatory cysts and bleeding
angiomyolipoma.
5

6. III. Growth rate:
• Growth rate of small renal masses is typically low (2 to 4 mm per
year) and seems to be similar for malignant (renal cell carcinoma) and
benign (oncocytoma).
6

7. IV. Tissue consistency:
• Areas of macroscopic fat within a renal mass are usually diagnostic of
angiomyolipoma
• Additional presence of calcification in a fat-containing lesion can
indicate a malignant condition.
• A small number of angiomyolipomas do not contain fat and remain a
diagnostic challenge as differentiation from malignant renal neoplasm
is impossible.
• Presence of central necrosis may be helpful in the diagnosis of RCC, a
finding that is very rare in angiomyolipoma
7

8. ULTRASOUND
• Patient body habitus, tumor echogenicity, size, and location
• Distortion of the normal tissue architecture
• Up to 77% of RCCs ≤ 3 cm are hyperechoic
• The rest are isoechoic or hypoechoic compared with normal renal
parenchyma
• Angiomyolipoma mainly appears as strongly hyperechoic on US due
to its fatty content.
• US characteristics of oncocytoma can vary greatly, cannot reliably
distinguish oncocytoma from RCC.
• Typical oncocytoma is with central scar
8

9. • 18% of tumors ≤ 2 cm are not detected on US
• Most challenging tumors to detect using US:
• small isoechoic renal tumors with endophytic growth pattern.
• Echogenicity of the tumor:
• does not differentiate between histologic subtypes and
• cannot reliably distinguish benign from malignant conditions
• Doppler USG added value in isoechoic endophytic tumors
(Detection ↑)
• Doppler US can show vessels with high velocity due to
neovascularization in case of RCC.
9

10. • Contrast-enhanced US (CEUS) is a technique in which a contrast
medium consisting of gas microbubbles is administered intravenously.
• It changes renal parenchyma more brighter on the grey-scale images.
Benefits of CEUS
• Provides information on the micro-circulation, unlike Doppler US,
which concerns macro-circulation.
• Contrast agents used for CEUS are not nephrotoxic.
• More sensitive in detecting hypovascular solid lesions
• In case of pseudotumors (prominent columns of Bertin, persistent
fetal lobulation, or dromedary hump) can be differentiated from renal
tumors because they show the same enhancing pattern as adjacent
renal tissue.
10

11. PSEUDOTUMORS
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12. 12

13. 13

14. • The enhancing pattern of angiomyolipoma and oncocytoma on CEUS
does not differentiate from RCC.
• Additional Doppler US or CEUS can be used to identify smaller
isoechoic, hypoechoic, and hypovascular tumors and can be used to
correctly identify pseudotumors.
• The ability of CEUS to characterize a lesion as benign or malignant is
undetermined.
14

15. COMPUTED TOMOGRAPHY
• Due to superiority over US and the lesser MRI availability, CT is often the
first choice of imaging for evaluation of a renal tumor.
3-phase CT scan
• Unenhanced phase  calcifications, fat, cystic hemorrhages, proteineous
fluids
• CMP  at 40-70 seconds delay  to assess tumor enhancement.
• NP  at 100-120 second delay  the tumor contrast washout and
provides information on possible tumor thrombus in the renal vein and
IVC.
• Excretory phase at 7-10 minute delay  to differentiate urothelial
cancer from RCC, parapelvic or peripelvic cysts from hydronephrosis, and
to diagnose calyceal diverticula.
15

16. Cysts and enhancement
Simple cyst
• Homogeneous lesion with a smooth wall
• No septa, no calcifications
• Attenuation between –10 and +20 HU on NECT
Hemorrhagic cyst
• Attenuation of >70 HU
CECT
• A lack of enhancement confirms the lesion to be cystic.
• After contrast administration, an enhancement of >20 HU in the CMP
(indeterminate and suspicious for RCC)
• Optimal sensitivity and specificity for RCC detection are reported when a
cut off value of 84 HU in the CMP and 44 in the NP
16

17. Accuracy
• For prediction of RCC from CT findings:
• Sensitivity - 60% to 79% and
• Specificity - 44% to 100% respectively.
• Findings may be influenced by tumor size:
• as 1 cm increase in tumor size is associated with a 16% increase in the odd of
malignancy.
• Intratumoral bleeding is sometimes hard to depict with CT.
• Only the diagnosis of classic angiomyolipoma can be made based on
CT alone.
17

18. MAGNETIC RESONANCE IMAGING
• Often used for characterization of indeterminate renal tumors on US
and CT
• Mainly suspected angiomyolipoma or moderate to non-enhancing
tumors suspected for pRCC.
• Gadolinium-enhanced sequences with fat saturation have more
sensitive than CECT  Tumors sized ≤20mm in diameter
• Calcifications can hardly to be seen on MRI.
18

19. • Intratumoral haemorrhage has a variable appearance depending on
the stage of degradation of the component blood products.
• Subacute haemorrhage demonstrates high signal intensity on both
T1- and T2-weighted images.
• Chronic haemorrhage, containing haemosiderin, is hypointense on
both T1- and T2-weighted image.
19

20. 1. Simple/Complex cyst
20

21. 21
Bosniak Description % Malignant Workup
1 Simple cyst 0% Nil
2 Minimally complex 0% Nil
2F Minimally complex
(need f/up)
5% USG or CT F/up
3 Indeterminate 50% Partial nephrectomy
4 Clearly malignant >95% Partial/ Total nephrectomy

22. 22

23. MRI presentation of typical image characteristics of a simple cyst (Bosniak I):
(a) hyperintense on T2-weighted images, (b) hypointense on T1-weighted images,
(c)no contrast media enhancement, and (d) bright on ADC map
23

24. MRI presentation of typical image characteristics of a complex cyst (Bosniak IV):
hyperintense with hypointense areas on T2- (arrow in a),
hypo- and isointense in T1- (arrow in b), focal contrast media enhancement on T1-
weighted (arrow in c), and heterogeneous pattern on the ADC map (arrow in d)
24

25. Clear Cell RCC (ccRCC)
• Most common type (70-80% of all RCC)
• Originate from epithelium of PCT
• Sporadic 95%, 5% associated with von Hippel-Lindau and tuberous
sclerosis
• 5 year survival rate – 44-69%
• 90% are hypervascular (mostly metastasis to lungs)
• Can be predominantly cystic.
25

26. • Propensity to invade vessels (45% of tumors)
• Tumor thrombus  Renal vein and inferior vena cava
• Higher tumor grade is correlated with:
• larger size,
• intralesional necrosis,
• retroperitoneal vascular collaterals,
• renal vein thrombosis,
• Interruption of the tumor capsule
26

27. CT
• CMP - Strong enhancement (mean 114±44 HU) d/t hypervascularization
• NP - Wash-out during the NP (mean 66±24 HU)  renal parenchyma
enhances more homogeneously and intensely than renal tumors
• Larger ccRCCs  heterogeneous due to necrosis, hemorrhage, and cystic
parts.
27

28. Gross appearance of clear cell RCC
28

29. Clear cell carcinoma best seen in nephrogenic phase
29

30. 30

31. MRI
• T1 - isointense compared with surrounding renal parenchyma.
• T2 - hyperintense (heterogeneous SI in large tumors d/t necrosis,
cystic degermation and hemorrhage)
• Heterogeneous enhancement after contrast administration in the
CMP (more avidly enhance than other RCC subtypes)
• Central Necrosis - homogeneous hypointense on T1 and moderate to
hyperintense on T2, no enhancement
• In 60% of ccRCCs, microscopic fat is present  drop in signal intensity
on opposed-phase images compared with in-phase imaging
31

32. Tumor Pseudocapsule
• Related to compression of the adjacent renal parenchyma by the
expanding tumor
• Hypointense rim on both T1- and T2-weighted images
• Interruption of this pseudocapsule correlates with invasion of
perirenal fat (advanced stage)
32

33. Papillary RCC
• 10%–15% of all RCCs
• Arise from distal convoluted tubules
• Well circumscribed, peripherally located
• May be multifocal(23%) and bilateral(4%)
• 75% of papillary RCCs are hypovascular
• Better prognosis than ccRCC (5-year survival rate of approximately
90%)
33

34. Gross appearance of papillary RCC.
Note typical cystic and hemorrhagic tumor with thick capsule.
34

35. CT
• Large papillary RCC  heterogeneous just like ccRCC
• Smaller tumors  more homogenous and subtle contrast
enhancement (+ 20 HU in the CMP) (Hypovascular tm)
• No enhancement is seen in up to 25% of the pRCCs.
• The wash-out effect is also not as distinct as in ccRCC.
35

36. MRI
• Larger tumors may be more heterogeneous because of hemorrhage,
calcification and necrosis.
• T1 – hypointense
• T2 – homogeneous low signal intensity d/t predominant papillary
architecture
• Both T1 and T2 low signal fibrous capsule – usually present.
• DWI - Restricted diffusion may be useful for differentiating from a
hemorrhagic cyst
• Compared with ccRCC, a less avid and slower enhancement pattern as
pRCC is hypovascular.
• 90% of all papillary tumours demonstrate a homogeneous or peripheral
enhancement pattern.
36

37. Papillary RCC Vs Clear Cell RCC
pRCC ccRCC
Vascularity Hypovascular Hypervascular
Enhancement Progressive Avid
T2 Low SI Higher SI
Microscopic Fat content Rare +
Chemical shift _ SI Drop on Opposed-
phase
Cystic portion Papillary projections
Hemorrhagic fluid
Internal mural nodule
Irregular walls & septa
Clear fluid content
37

38. Bean-type hypovascular left renal mass
Biopsy: pRCC
38

39. Bean-type hypovascular left renal mass
Biopsy: pRCC
39

40. Chromophobe RCC
• 5% of RCCs
• Arise from intercalated cells of collecting ducts
• 5 year survival rate – 78%-93% (best prognosis among RCC subtypes)
• Cystic change and central necrosis may be absent even in very large
chromophobe carcinomas.
• Moderate enhancement
• chrRCC – histologically similar to oncocytoma (overlapping histologic
and imaging features)
• Imaging features can be identical to those of clear cell RCC
40

41. Imaging Features
• Appears well circumscribed and homogeneous on MRI
• T2 - intermediate to low signal intensity
• The enhancement pattern of chrRCC is more avid than in pRCC and
less avid compared with ccRCC. (Intermediate)
• Overall, the differentiation of chrRCC based on MRI remains
challenging due to its overlap with other subtypes.
41

42. Gross appearance of chromophobe RCC.
Light brown uniform tumor in one pole of kidney.
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44. 44

45. 45

46. Imaging presentation of a papillary (upper row) and a chromophobe (lower row) RCC.
Papillary RCC (a: CT venous phase; b: T2-weighted; c:T1-weighted, venous phase)
Chromophobe RCC (d: NECT ; e: arterial phase; e: venous phase)
46

47. Transitional Cell Carcinoma
• Less common in upper urinary tract
• 90% arise from renal pelvic
• Frequently multifocal
• Lymphatic metastasis occur early
• T1 – isointense to renal medulla
• T2 – hypointense filling defect in collecting system infiltrating renal
parenchyma
• Enhancement of focal filling defect in the collecting system – strongly
suggest TCC.
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48. 48
TCC with periureteral involvement in a 54-year-old
woman with right flank pain
(a) Coronal MIP image from contrast-
enhanced MR shows:
- mild right hydronephrosis with blunting of
the calices in the middle of the right kidney
and an irregular mass (arrowhead) in the
central portion of the kidney.
- proximal and middle portions of the ureter
are not visualized (arrows).
(a) Coronal contrast-enhanced 3D
nephrographic phase fat-saturated GRE
T1-weighted MR image shows:
- thickening and irregularity of the proximal
ureter (arrowheads).

49. Lymphoma
• Renal involvement by lymphoma may be due to hematogenous
dissemination or contiguous extension of retroperitoneal
disease
• Primary renal lymphoma is rare
• Non-Hodgkin lymphoma is much more common in the kidney
49

50. Imaging Features
USG
• hypoechoic lesions (single/multiple)
• within renal parenchyma with very little vascularity
50

51. 3 pattern of Renal Lymphoma
1. Multiple homogeneous masses with low level enhancement (60% of
cases)
- 1-3cm, associated with enlarged retroperitoneal nodes
2. Single bulky retroperitoneal mass, which may extend directly to and
encase one or both kidneys (20% of cases).
- Up to 15 cm
- Homogeneous hypodense without cystic change
3. (Less commonly) Infiltrative pattern  nephromegaly without disruption
of the renal contour.
- No discrete mass
- Usually bilateral
There may be peri-pelvic and periureteral disease that manifests as wall
thickening and enhancement.
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52. MRI
• T1 - Hypo- to renal parenchyma
• T2 - iso- or hyper- to renal parenchyma
• Gad - poor enhancement compared to renal parenchyma
- delayed enhancement in some lesions
52

53. 53
Sagittal T1 contrast-enhanced fat-saturated
(excretory phase) reveals a well-defined,
homogeneous, hypoenhancing mass (arrows).
Lymphoma was confirmed with percutaneous
biopsy

54. Non-Hodgkin follicular B-cell lymphoma involving the renal pelvic wall and renal sinus in a
58-year-old woman.
• Sagittal T1-weighted contrast-enhanced (excretory phase data ) MR image shows soft-
tissue thickening and enhancement of the wall of the renal pelvis (arrowheads).
54

55. Malignant mesenchymal renal tumors
• Primary renal sarcomas of adult kidney - Rare
• 1-3% of all malignant renal tumors
• Three basic criteria should be met.
1) Exclusion of renal metastasis from sarcoma elsewhere in the body
2) Confirm renal origin rather than involvement with retroperitoneal sarcoma
3) Exclusion of sarcomatoid RCC
4 Malignant mesenchymal tumors of kidney:
1) Leiomyosarcoma
2) Synovial sarcoma
3) Osteosarcoma
4) Fibrosarcoma
55

56. Leiomyosarcoma
• 50-60% of all renal sarcoma
• Arise from renal capsule, parenchyma, smooth m/s fibers of renal
pelvis or main renal vein
• 40-70 yrs, M=F
• Expansile well-defined solid mass with heterogeneous enhancement
• Delayed enhancement of fibrous stroma
56

57. Angiomyolipoma
• Most common benign solid renal tumour
• Mostly 4th-6th decades, Female predilection (2:1)
• Hamartomas containing varying proportions of fat, smooth muscle
and thick-walled blood vessels.
• Presence of macroscopic fat is pathognomonic of AML
• Tumours larger than 4 cm has increased risk of life-threatening
haemorrhage (up to 10% of these patients)
• 80% of AMLs – sporadic, 20% associated with tuberous sclerosis
57

58. CT
• Typical diagnosis based on non-enhanced CT findings.
• CT attenuation of –10 HU or less is pathognomic for AML
• 5% are fat-poor (absence of fat does not rule out the possibility of
AML)
• Calcifications should raise the suspicion for RCC.
• Enhanced on CECT
(cannot be differentiated from RCC by CT imaging alone, and additional MRI,
biopsy, or surgical resection might be warranted)
58

59. 47-year-old woman with Angiomyolipoma
- Some streaks of soft tissue within the lesion, corresponding with
vascular and smooth muscle components (arrowheads)
59

60. MRI
Classic AML
• High on T1-weighted and low on fat-suppressed MRI sequences.
• A low-signal intensity rim at the interface between AML and renal
parenchyma can be seen when opposed phase MRI is used.
• Is called the “India ink artifact” (chemical shift artifact) and is typical
for angiomyolipoma.
• The classic angiomyolipoma enhances quickly with a fast wash out
effect.
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61. India Ink Artefact
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62. Fat-poor Angiomyolipoma
• Challenge to differentiate from RCC.
• 5% of AMLs
• Low fat content and similarity to smooth muscle SI  Hypointense on
T1- and T2WI
• Fat-poor angiomyolipoma shows an early homogeneous
enhancement pattern with rapid wash out.
• T2 hypointense may mimic pRCC, a subsequent biopsy to confirm the
diagnosis is advised.
62

63. Oncocytoma
• 3–7% of solid renal masses, Size – may up to 12 cm in diameter
• More common in men, Mean - 7th decade
• May be multicentric, bilateral or metachronous (minority)
• Well-defined hypointense capsule can be seen surrounding the
tumour in almost one-half of renal oncocytomas.
• Central scar appears in 50% to 60%, but is not a specific finding for
oncocytoma.
• Absence of calcification, necrosis or hemorrhage suggests the
diagnosis.
• Histologically difficult to differentiate from chrRCC.
• Also increased association of clear cell RCC.
63

64. Imaging
• The imaging characteristics of oncocytoma are variable and overlap
greatly with RCC, especially with those of chrRCC.
• Low SI on T1 relative to renal cortex
• High and heterogeneous signal intensity on T2
• Central scar – Low SI on T1, High SI on T2 with delayed Gd
enhancement
• Contrast (Stellate or spoke wheel pattern of enhancement)
64

65. Gross appearance of renal oncocytoma.
Homogeneous mahogany brown contour with encapsulation.
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68. 68

69. The patient was treated with percutaneous image-guided cryoablation.
Intraoperative biopsy specimens showed an oncocytoma.
69

70. Juxtaglomerular Cell Tumor (Reninoma)
• Rare benign lesions derived from juxtaglomerular cell
• Predominantly in women, 3rd or 4th decade
• Present with hypertension with hypokalaemia d/t renin hyper
secrection
• T1 – iso SI, T2 – high SI
• Low-level enhancement after Gd administration
70

71. 71
CECT during the nephrographic phase shows an expansile mass (arrow)
with soft-tissue attenuation in the right kidney.
At histologic examination after surgical excision, this mass was
determined to be a juxtaglomerular cell tumor.

72. 72
Juxtaglomerular cell tumor (reninoma) in a 27-year-old woman with hypertension.
(a) Coronal steady-state fast spin-echo T2-weighted MR image shows a small mass (arrowheads) in the
central portion of the right kidney. The mass was almost imperceptible during the corticomedullary and
nephrographic phases, when it enhanced to the same degree as the renal medulla.
(b) On a coronal contrast-enhanced delayed excretory phase image, the mass is homogeneous and
demonstrates lower signal intensity than that of the adjacent renal parenchyma. Although the imaging
findings of a hypovascular central mass are nonspecific, a clinical manifestation of hypertension is
helpful, and the possibility of reninoma should be considered.

73. Lymphangioma
• Aka renal lymphangiectasia or renal lymphangiomatosis
• Common in adults, no gender predilection
• Rare benign renal tumor
• Developmental anomaly of peri-renal lymphatic system rather than
true neoplasm
• Well-encapsulated multilocular cystic mass in perinephric or renal
sinus region
• T1 – hypointense, T2 – uniformly hyperintense
• SI of intra-cystic fluid may be variable (H’ge, debris, protein content)
• Linear tortuous fluid-filled structures in retroperitoneum  dilated
lymphatic channels
73

74. 74
CECT image shows:
bilateral multiple cystic masses in the perinephric (white
arrow) and renal sinus (black arrow) regions, consistent
with lymphangiomas.
Lymphangioma in a 45-year-old man.
Coronal T2-weighted MR image shows bilateral
multilocular cystic masses (arrows) in the
perinephric and renal sinus regions, consistent with
lymphangiomas.

75. Solitary Fibrous Tumor
• Previously classified as hemangiopericytoma
• Commonly arise in pleura
• In kidney, arise from renal capsule
• Age - >40 years, slight female predilection
• Most are benign, malignancy about 10%-15%
• Large, homogeneous, well-circumscribed firm mass
75

76. CT
• Well-circumscribed soft-tissue mass in renal sinus or capsule
• Relatively homogeneous enhancement despite large size of the mass
• Necrosis and cystic changes are uncommon.
76

77. 77
Contrast-enhanced CT image shows a lobulated hypoattenuating
heterogeneous soft-tissue mass (arrow) in the left kidney.
At histopathologic examination, the tumor was determined to be a solitary
fibrous tumor.

78. MRI
• Large, well-circumscribed mass
• T1 – homogeneous and isointense relative to renal capsule
• T2 – alternate areas of extremely low SI and moderate high SI
(distributed in radial configuration)
• Relatively hypovascular  limited enhancement in arterial,
heterogeneous spoke-wheel pattern enhancement in delayed phase
78

79. 79
Solitary fibrous tumor of the renal capsule in a 51-year-old woman.
(a) Coronal steady-state fast spin-echo T2-weighted MR image shows a large, well-
defined mass (arrows) with predominantly low signal intensity.
(b) Oblique sagittal contrast-enhanced excretory phase fat-suppressed T1-weighted MR
image shows the mass with heterogeneous enhancement, although no central
necrosis is appreciated.

80. NUCLEAR IMAGING
Positron emission tomography
• 18 FDG PET/CT is not recommended as a primary diagnostic imaging
modality for RCC
• low sensitivity (62%) and specificity for detection and characterization
80

81. Immuno-imaging using Girentuximab
• Girentuximab is a molecular antibody recognizing carbonic anhydrase
IX (CAIX), a specific antibody present in 94% of ccRCCs.
• SPECT-CT using indium-111-labeled-girentuximab is a feasible
diagnostic tool for ccRCC, with a positive and negative predictive
value of 94% and 100% respectively.
• Using iodine-124-labeled-girentuximab PET-CT (sensitivity and
specificity of 86%)
81

82. (A) 3-phase CT scan showed an interlobular heterogeneous mass in the left renal cortex. Avid
enhancement of the solid parts is seen in the corticomedullary phase, especially in the solid tumor parts,
making this tumor suggestive for renal cell carcinoma.
(B) An additional MRI with T2-weighted fat saturated sequences acquired in the coronal plane showed a
heterogeneous renal mass with growth towards the renal pelvis. Note the simple cysts in the lower pole.
(C) Additional SPECT/CT 5 days after administration of 111-Indium-Girentuximab shows targeting of the
renal tumor making a clear cell subtype highly likely. A second hot spot in the renal pelvis was noted.
Histopathology after laparoscopic radical nephrectomy confirmed the diagnosis of a 50mm large, Furhman
grade 3, clear cell renal cell carcinoma.
82

83. Technetium-99m-sestamibi SPECT-CT
• Technetium-99m-sestamibi SPECT-CT for accurate differentiation of
oncocytomas and hybrid oncocytic/chromophobe tumors from other
RCC subtypes.
• Oncocytomas/hybrid oncocytic/chromophobe tumors show higher
uptake compared with RCC.
83

84. CONCLUSIONS
• Differentiation of renal tumors is important to facilitate treatment
planning.
• US can be used as a screening tool for renal tumors, but smaller
endophytic tumors can be missed during screening.
• Additional Doppler or CEUS can be used to identify smaller isoechoic,
hypoechoic, and hypovascular tumors and correctly identify
pseudotumors.
• CT is able to differentiate classic AML from malignant entities.
• Sensitivity for CT to discriminate RCC subtypes, fat-poor
angiomyolipoma, and oncocytoma is remain challenging.
84

85. • Multiparametric MRI is able to discriminate classic angiomyolipoma
from RCC and differentiate RCC subtypes.
• The differentiation of fat-poor angiomyolipoma is challenging and
often still warrants a biopsy.
• Oncocytoma cannot be reliably distinguished from RCC.
• The availability of nuclear imaging for renal tumors is very limited.
• But, these modalities show promising results for the differentiation of
ccRCC and oncocytoma.
• Only the diagnosis of classic AML can be made based on CT or MRI
alone.
• A biopsy prior to surgery may be best suitable for smaller renal
tumors as relatively high incidence of benign lesions among this
group which cannot be discriminated by imaging.
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91. 91

92. Clinical flow chart of renal masses
92

93. Steps in the differentiation of a renal lesion
• Cystic lesion?
• If it is not a cyst, look for macroscopic fat, which means that it is a
benign angiomyolipoma (AML).
• Calcification usually suggestive of being malignant lesion.
• Exclude tumor-mimics like infection and infarction, which usually
present in different clinical settings.
• Exclude metastatic disease and lymphoma; kidney localizations are
usually only seen in widespread disease.
93

94. Low T2 SI
• Low T2  pRCC, lipid-poor AML, hemorrhagic cyst, metanephric
adenoma
• Low T2 + enhancement  exclude hemorrhagic cyst.
• Low T2 + progressive enhancement + SI drop on in-phase relative to
opposed-phase  suggest hemosiderin  most likely pRCC.
• Low T2 + avid or moderate enhancement + SI drop on opposed-phase
 suggest Lipid-poor AML
94

95. High T2 SI
• High T2 + hypervascularity + Signal drop on opposed phase
(microscopic fat)  ccRCC, classic AML
• Central necrosis often (+) in ccRCC.
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96. THANK YOU
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